Aiming at a low carbon society, mass introduction of apparatuses for generating electric power with natural energies, such as the solar photovoltaic generation (PV) and the wind power generation is expected. Since it is often the case that these are installed being distributed geographically compared with existing concentrated power sources, such as thermal power generation, hydraulic power generation, and nuclear power generation, they are called dispersion type power sources or the distributed power sources. Generally, whereas a consumer purchases and uses electric power that the concentrated power source supplies via the electric power system, a consumer having the distributed power source can use electric power that is generated in house for self-consumption. Then, the consumer purchases (buys) shortage power and can supply (sell) surplus power to the electric power system and can allot obtained money to recovery of a purchase expense of the distributed power source.
The electric power system is configured with many power sources, loads, impedances of the system itself, etc. combined together intricately. In a situation where each has a fluctuation factor, it is an important issue to perform stabilized electric power supply to the customers. A situation where the system voltage fluctuates causes an excessive voltage or current to be applied to the facility apparatus that is included in the electric power system, which may become a factor of degrading an apparatus characteristic, shortening its life, or the like. Moreover, it may become a destabilizing factor of an operation of the apparatus that the consumer possesses. Then, for example, a low-voltage system of electric power distribution has a system voltage range requirement of 101±6V. Conventionally, with the aim of maintaining stabilized operations of the system itself and linked apparatuses and suppressing a voltage fluctuation by loads etc., voltage stabilization technologies have been developed. For example, voltage control apparatuses, such as a load-time tap switching potential transformer (LRT), a step voltage control apparatus (SVR), and a static var compensator (SVC), are known.
However, the distributed power source has a different characteristic from that of the existing concentrated power source. First, an amount of power generation of the distributed power source using these natural energies fluctuates depending on climate conditions, such as the amount of solar radiation, a wind direction, and a wind force. Moreover, generally, the voltage falls as a position of the electric power system goes closer to its end, but the voltage on the end side of the system may rise by the distributed power source supplying surplus power to the electric power system. A combination of these characteristics will result in a fluctuation of the system voltage depending on the climate conditions.
A representative technology of suppressing deviation of the voltage from a permissible range in the electric power system to which the distributed power source is connected will be shown. In a technology described in Patent Literature 1, a fluctuation of the system voltage based on a weather forecast is predicted, and a voltage control by supplying a reactive power of the PV apparatus (PCS) is performed. In a technology described in Patent Literature 2, a system voltage distribution is inferred based on future weather information and judged whether electric power supply by a voltage regulator shall be done or not. In a technology described in Patent Literature 3, when there is a voltage rise by a reverse tidal current by PV power generation, switching by a switch is performed.